The present invention relates to grayish-black encapsulated pigments based on zirconium silicate as the casing substance into which colored compounds are encased as a discrete phase. The present invention also relates to a method of producing these encapsulated pigments.
Encapsulated pigments or inclusion pigments have become known, in the prior art as, for example, from DE-PS 23 12 535. They consist essentially of transparent crystals of glaze-stable substances such as e.g. zirconium silicate, zirconium oxide or tin oxide into which inorganic, moisture-free, colored compounds are included or encapsulated as a discrete phase. Thenard's blue (cobalt blue), titanium yellow and especially cadmium yellow and cadmium red are examples of colored compounds. Zirconium iron rose with Fe.sub.2 O.sub.3 inclusions in a zirconium silicate casing is also known.
The production of these encapsulated pigments takes place by means of heating the casing substances or their precursors and the colored substances to be included or their precursor compounds in the presence of one or more mineralizers to temperatures up to 1200.degree. C. However, it was found that not all conceivable colored compounds can be encapsulated into the casing substances in an appreciable yield with this prior method.
The palette of grayish-black colors is not very large. Gray and black bodies are obtained essentially from iron oxides and chromium oxides, optionally in combination with other oxides such as e.g. manganese oxide, copper oxide, nickel oxide or cobalt oxide. Grayish-black encapsulated pigments were not known in the past.